As no moving component is provided in the cold finger part, the pulse tube refrigerator is much more reliable compared with the traditional G-M refrigerator and the Sterling refrigerator; the cold finger has advantages of no wear, low vibration, low noises and so on and has extensive commercial application values.
The pulse tube refrigerator can be regarded as the variant of the G-M refrigerator which takes place the solid piston with the gas piston and obtains refrigeration effect via the insulating discharge and expansion process of the high pressure gas in the hollow cavity of the pulse tube.
The work process thereof comprises:    1) Air intake process: The inlet valve is open, the high pressure gas flows through the heat regenerator, the cold end heat regenerator and the fluid director via the valves, enters into the pulse tube in laminar flow way and pushes the gas in the tube toward the closed end. The gas is extruded and enable the gas temperature in the closed end of the pulse tube to reach the maximum value.    2) Heat exchange process: The water cooler installed in the closed end of the pulse tube takes the heat away so as to reduce the temperature of the gas in the tube to the original temperature when entering the heat regenerator.    3) Air discharge process: The discharge valve is open and is connected with the low pressure air pipe, the gas in the pulse tube is expanded to generate refrigeration effect, the temperature of the gas is reduced to the minimum temperature.    4) Heat regenerator process: The expanded low pressure gas flows through the heat regenerator reversely, absorbs the heat in the filler, goes back to the compressor inlet and finishes a circulation. Refer to FIG. 1.
The general expression of the refrigerating capacity of expansion refrigeration by the gas in the pulse tube is as follows:{dot over (Q)}=∫pd{dot over (V)}
The refrigerating capacity thereof is determined by the pressure p reaching in the pulse tube, flow v and the phase relation between them. In the G-M pulse tube refrigerator, the phase relation between the pressure and flow can be interpreted as the relative time span of the gas compression process or expansion process.
No moving component is provided in the cold end of the pulse tube refrigerator, therefore the flow and phase of the gas entering the pulse tube cannot be regulated actively; an active air distribution device must be provided in order to obtain an ideal relation between the flow and phase at super low temperature, for example the double-stage pulse tube refrigerator with six valves for actively air distribution as shown in FIG. 2.
The plane rotary valves are used as the traditional air distribution valves, and the valves are designed on a moving device. Once the design and manufacture of the plane rotary valves are finished, the gas flow and open/close time and sequence of the valves cannot be changed; when the refrigeration temperature is changed by working condition changes, the refrigerator cannot reach the best operating parameter by regulating the flow and phase of the gas. In addition, during the operation process, if dusts enter into the pipes, for example the holes and pipes of the two-way inlet valve, the flow coefficient will be changed, thereby the flow and phase of the gas in the refrigerator is changed and deviated from the best operation parameter of the original design.
As the refrigeration temperature of the pulse tube refrigerator is easily influenced by many factors such as change of the environment temperature, impurity in the internal gas and direction of the cold finger, unstable situations occur easily in the operation process. Therefore, the flow and phase of the gas entering the heat regenerator or pulse tube need to be regulated respectively in accordance with these factors during the operation process of the refrigerator so as to regulate the performance of the refrigerator, enable the refrigerator to be in the optimized working condition and enhance the efficiency of the refrigerator and stability of the refrigeration temperature.